Duncan has just been murdered and his sons are watching people weep and wail as if the loss were too great to bear while their own tears remain unshed--they are too shocked and too vulnerable to give them liberty. They suspect that someone in the castle is responsible, and they have reason to mistrust (and fear) everyone that they thought were "friends." There is no way for them to know who the murderer is--especially since Macbeth has just killed the sleepy (drugged) blood smeared "murderers" in a fit of righteous rage (or so he claims). We know otherwise.

My reading of this line is that the "daggers in men's smiles" suggest that the people will smile to their face but those very smiles could kill them. Duncan, their father, was not a good judge of character. He even admitted that, saying of his misplaced faith in the original Cawdor that "there's no art/ to find the mind's construction in the face". In contrast to their innocent father, Malcolm and Donalbain understand that some people may appear friendly but have evil intentions.

In the context of Donalbain's other words, it seems clear that he means that they are unsafe in present company. He refers to the necessity of separation to ensure their safety and, immediately after the dagger reference, says that the "nearer the blood, the nearer bloody" (which I take to mean that he is aware that the closer he stays to this place where his father was killed and men smile daggers, the more likely he is to be killed himself.

A good question. As with many of Shakespeare's great lines, it refers to a physical reality and a deeper meaning.

The physical reality? People have pointed teeth (some of them).

The deeper reality? People sometimes smile to deceive you, when they really mean to attack you. The smile is then a sign of betrayal. Since Donalbain says this line, after his father's death, it means he distrusts Macbeth's show of mourning/ sympathy.

This part of a line is spoken by Donabalin in 2.2.120-121. The entire line reads, "Where we are,/There's daggers in men's smiles."

Donalbain is speaking to Malcom. Both are King Duncan's sons. Macbeth, to steer attention away from himself after murdering Duncan, has killed the grooms that had accompanied Duncan and his sons to Macbeth's castle. He falsely accuses the groomsmen of Duncan's murder.

Macbeth simulates great grief but the son sees through him. This is why Donalbain cautions, "There's daggers in men's smiles." Fearing that he and his brother will suffer the same fate as his father and the groomsmen, the pair flee the country.

Its important to note that this a continuation of the theme of deceit that Shakespeare began earlier in the play. In the beginning of Act II, Lady Macbeth tells Macbeth he must "look like the innocent flower/yet be the serpent under it." She is instructing him to show a false face to the world, looking innocent but being dangerous. He takes her advice, but Donalbain lets us know that he sees through that disguise.

A good question. As with many of Shakespeare's great lines, it refers to a physical reality and a deeper meaning.

The physical reality? People have pointed teeth (some of them).

The deeper reality? People sometimes smile to deceive you, when they really mean to attack you. The smile is then a sign of betrayal. Since Donalbain says this line, after his father's death, it means he distrusts Macbeth's show of mourning/ sympathy.

okay honestly you dont have read mcbeth to know what this means.. there are daggers in men's smiles - a quote in which explains this world. a quote that speaks the truth about things.. it means that something as simple as a smile is so deciving... and has been for since this world has started. it means that your best friend can be your worst enemy.... and so it goes on